1. Field of the Invention
The present invention relates to a power supply control system and a method controlling a power supply.
2. Description of the Related Art
The number and kinds of electronic devices provided in a vehicle tend to increase year by year. The electronic devices are jointly controlled by a plurality of control devices that is coupled through a communicating line. Even when a control device that takes charge of controlling respective electronic devices is different from one electronic device to another, a power supply system is often shared by the control devices. For example, the control devices for controlling the electronic devices provided in the vehicle are coupled with a battery equipped in the vehicle through a power source line. When the total amount of electric current that flows in the power source line, i.e., the total amount of consumption current of all the control devices exceeds a threshold current value, a fuse provided on the power source line may be blown out and the power supply to all the control devices may be cut off.
In the present case, the threshold current value is fixed based on a property of the fuse regardless of an operating state of each of the control devices. Specifically, a maximum current value is calculated for each of the control devices and the total amount of the maximum current values is set as the threshold current value for disconnecting the power source line. However, an actual maximum current value of each of the control devices may vary in accordance with a position of an ignition switch. When the ignition switch is set at an IG-ON position, an engine of the vehicle is activated. When the ignition switch is set at an IG-OFF position or an ACC-ON position, the engine is deactivated. When the ignition switch is set at the IG-OFF position or the ACC-ON position, some connected load may be deactivated. Thus, some control devices may transfer to a sleep mode (i.e., power-saving mode). In the sleep mode, the control device may have a back up of control parameters using a random access memory (RAM) and a clock operation of a central processing unit (CPU) may be stopped. When the control device is set to the sleep mode, a current value to be determined as an abnormal current value may be much lower than that in a run mode in which the control device is normally operated and the clock operation of the CPU is performed. However, even when the control device is set to the sleep mode, the threshold current value for disconnecting the power source line remains a high current value that corresponds to the run mode. In the present case, the power source line can be disconnected when the power source line is shorted and a high electric current will apparently flow. However, if the clock operation of the CPU is continued, for example, due to a runaway, in the control device that should be at the sleep mode, and thereby the current value becomes an abnormal level at the sleep mode, the power source line is difficult to be disconnected when the current value is within the normal level at the run mode. Thus, a battery drain may be caused by the runaway.
JP-A-2000-236621 and JP-A-2000-245055 respectively disclose a power supply control system that sets a threshold value for disconnecting a power source to be variable. The threshold value is varied in accordance with an operating state of a plurality of electronic devices coupled with one control device configured by a microcomputer or the number of connected load. In the present case, a power source disconnecting unit is provided to each of the control device. Thus, a cost of the power supply control system may increase.